A steel building in the Tennessee Valley sweats. Warm humid air meets cold metal and it rains inside. Closed-cell spray foam on the panels is the fix that also insulates and stiffens the building.
Tell us what the Chattanooga property is doing and we'll take a look.
Steel has almost no insulating value and it changes temperature fast. On a spring night the roof panels of a shop or barn radiate heat to a clear sky and drop below the dew point of the air inside. With Chattanooga's morning humidity averaging around 85 percent in NOAA's long-term records, that air has plenty of water to give up, and it condenses on the underside of the roof and runs down the purlins. Shop owners around Hamilton County and the North Georgia counties know the pattern: rusty tools, wet floors, stained inventory, and a building that is unusable in August and miserable in January.
Fiberglass blanket insulation with a vinyl facing, the kind that comes with most metal building kits, slows this down but does not stop it. The facing tears, the seams open up, and moisture gets behind it and sits against the steel. Once it is wet it stays wet.
Closed-cell spray foam bonds directly to the metal panels and purlins and cures into a rigid, seamless layer. Because it is closed-cell it does not absorb water, and at about two inches it acts as a vapor retarder, so warm interior air never reaches the cold steel. The condensation stops, not because the air is drier but because the cold surface is no longer exposed to it.
At the same time you get about R-6 to R-7 per inch of real insulation, which means a two-inch application delivers roughly R-13 and a three-inch application roughly R-19 to R-20. That is enough to make a shop heatable and coolable with equipment sized for the space instead of for a tent. Closed-cell also adds rigidity to the panels. Roofs and walls flex less in wind, and the drumming noise of rain on a metal roof drops off sharply.
We spray the roof panels, the walls to whatever height the use calls for, and the joint where the wall panels meet the slab or grade board, which is where most of the air leakage in a metal building happens.
Post-frame buildings are common across the rural edges of the metro, out past Ooltewah and Apison, up toward Soddy-Daisy and Sale Creek, and down through Catoosa and Walker counties in Georgia. They are being finished into workshops, gyms, offices, hobby garages and living space more often than ever. The difference between a pole barn that works as a finished space and one that never does is almost always insulation and air sealing.
In a post-frame building the roof is usually metal on purlins with an open framing cavity and the walls are metal on girts with no sheathing. Closed-cell on the metal is the standard approach for both. If the owner plans to finish the interior with drywall or metal liner panel, we coordinate the foam depth with the finish so nothing has to be trimmed later. Where the building will stay open-framed, the foam has to be covered with an ignition barrier or an approved intumescent coating, and the scope spells out which.
Horse barns and livestock buildings are a special case because animals produce a lot of moisture and ammonia. We talk through ventilation with you before recommending anything, because a tight, insulated barn with no air exchange is worse than an open one.
Existing blanket insulation comes out first. Steel gets checked for oil, dirt and loose rust, and cleaned where needed, because foam adhesion is only as good as the surface. Lights, outlets, garage door tracks and anything else that needs to stay accessible get masked or relocated ahead of time. Panels should be dry and within the manufacturer's temperature range on spray day.
After the foam cures, exposed foam in an occupied building generally needs a thermal barrier or an approved intumescent coating. In an agricultural building used only for storage the requirement may differ, and the local building official has the last word. We will tell you what applies to your building and your county, and include the coating in the scope where it is needed rather than leave it as a surprise.
Questions
Two inches of closed-cell is the usual minimum because that is where it acts as a vapor retarder and stops condensation. Owners who plan to heat and cool the space year-round often go to three inches on the roof for the added R-value. The scope prices both so you can choose.
No. It has to come out. Foam needs to bond to the steel, and blanket insulation that has been in place through a few Tennessee summers is usually holding moisture against the panels anyway.
Closed-cell foam keeps moisture away from the steel, which is the opposite of rusting it. Problems come when foam is sprayed over panels that are already wet or corroded, which is why the panels are inspected and dried first. If your roof has active leaks at fasteners or seams, those get fixed before anything is sprayed.
Yes. Curved steel is actually a good candidate because blanket insulation is so hard to fit to it. The foam conforms to the curve and bonds to the ribs. Access and lift equipment are the main planning items.
Tell us what the house is doing and where. We will come look, measure and write a scope you can compare.
Request a free estimate Call (423) 564-5601